The present invention relates generally to the art of winding equipment. More specifically, the invention relates to an apparatus and a method of producing rolls of plastic bags, in which the bags are wound into a roll without being connected to one another.
Many different types of winding machines are known for winding pliable strips of material such as plastic bags. One type of apparatus is arranged to wind bags into a roll without the bags being connected to one another. In this apparatus, a bag is separated from a continuous web of bag material having perforations in the boundary between adjacent bags. A leading end of the separated bag is arranged to overlap a trailing end of a preceding bag, thereby building a strand of so-called interleaved bags. This strand of bags is then wound into a roll in a winding device.
One such roll-forming apparatus, as disclosed in U.S. Pat. No. 5,377,929, has a tumbler assembly which is arranged intermediate a feeding device and a winding device. The tumbler device is adapted to receive a continuous web of bag material from the feeding device. By rotating the tumbler assembly, a bag is separated from the web and arranged to partly overlap a trailing end of the succeeding web fed from the feeding device. The strand of interleaved bags thus formed is fed to the winding device, in which a roll of bags is formed.
U.S. Pat. No. 4,000,864 discloses a roll-forming apparatus in which a gripping device is arranged intermediate a feeding device and a winding device. The gripping device is adapted to grip the leading edge of a separated bag as received from the feeding device, accelerate the separated bag relative to a preceding bag, decelerate the separated bag and place a leading end of the separated bag on a trailing end of the preceding bag. This operation is repeated to form a strand of interleaved bags which are fed to the winding device.
U.S. Pat. No. 4,034,928 discloses a roll-forming apparatus having a sheet tuck-in means in the form of a blade. In this apparatus, separate bags are fed to the tuck-in means, where a bag is folded by advancing the blade into contact with the bag about midway between its terminal edges. Then a succeeding bag is fed to the tuck-in means, folded and advanced such that it is caught between the terminal edges of the preceding bag. Thus, a strand of interleaved bags is created. This strand is fed to a winding device, in which a roll of bags is formed.
One drawback of the above types of apparatus resides in their inherent mechanical complexity. Thus, the prior-art roll-forming apparatus tends to be expensive, have much down-time and require frequent maintenance. Further, the apparatus often includes a sophisticated control system for adequate timing of the feeding and overlapping operations. Expensive and delicate sensors might also be installed to provide necessary timing signals. Also, the overlapping operation often calls for a periodic and abrupt change in the speed of various feeding mechanisms, leading to increased wear and tear in the machinery.
Other related prior art is disclosed U.S. Pat. No. 5,779,180, WO 97/33744, and DE-A-37 42 994, the latter disclosing a device for producing a stack of plastic bags. The stacking device includes a rotating barrel drum, the periphery of which has a projecting needle. Separated bags are sequentially fed to the barrel drum, where they are threaded onto the projecting needle, thereby creating a stack of overlapping bags on the periphery of the drum. By stopping the drum and retracting the needle, the stack of bags can be transferred to a subsequent discharge device.
One object of the invention is to solve or alleviate some or all of the above problems associated with the prior art. More specifically, it is an object of the invention to provide a roll-forming apparatus of simple construction, which is capable of winding bags into a roll without the bags being connected to one another and without inflicting any damage to the bags.
Furthermore, the apparatus should exhibit low wear and tear of the included components.
A further object is to provide a roll-forming apparatus with little need for control and timing in the production of rolls of bags.
Still another object is to provide an apparatus allowing for little down-time and high production rates.
An additional object of the invention is to provide an apparatus capable of being included in or operated together with conventional bag-making machines.
Another object of the invention is to provide a method remedying some or all of the drawbacks described above.
These and other objects and advantages of the invention, which will appear from the description below, are achieved by an apparatus and a method as set forth in the independent claims. Preferred embodiments are defined in the dependent claims.
The invention is based on the understanding that one can dispense with the arranging of the separated bags in an overlapping fashion before winding them into a roll of bags. Instead, the feeding means is arranged to feed bags one by one to the winding station. The winding station includes a rotating spindle which is arranged to engage with each bag, directly or via bags previously wound thereon, to form the roll of bags in which the bags are unconnected to one another yet firmly held together. This allows for considerable simplification in the construction of the apparatus. Since the bags are fed one by one to the winding station, there is no need for tumbling or reciprocating devices manipulating the leading or trailing ends of each bag. Thus, a reduced risk of damage to the bags results, as well as low wear and tear in the construction itself. Further, since the bags are fed one by one to the winding station, it is easy to direct the flow of separate bags between different winding stations. This allows for high production rates since two or more winding stations can be operated sequentially such that a roll of bags is being formed in one winding station while a finished roll of bags is being discharged from an adjacent winding station.